1. Field of the Invention
The present invention relates generally to a measurement tool for determining the number of packing material rings that are required to fill and seal a stuffing box cavity surrounding a shaft. More particularly, the present invention relates to a graduated ruler for indicating the number of compressible packing rings and/or non-compressible bushing rings that are required to fill and seal a stuffing box cavity surrounding a shaft.
2. Background of the Related Art
Compression packing is used to control leakage about shafts. Compression packing generally comprises an assembly of radially expandable rings that coaxially surrounds a shaft. Such packing is used in a wide variety of applications including packing for pumps, valves and hydraulic and pneumatic equipment.
Shafts are conventionally surrounded by a compartment generally extending outwardly from the housing surrounding the shaft referred to as a "packing box" or "stuffing box." The interior of the stuffing box is generally of a diameter sufficiently greater than the shaft to accommodate compressible "packing rings" and relatively non-compressible bushing rings. The packing rings in the stuffing box are generally compressed by a annular "gland" fitted about the shaft and bolted to the exterior of the stuffing box. Axial compressive loading force from the gland is applied to the packing rings causing them to expand radially to some extent, forcing the inner peripheries against the outer surface of the shaft and causing the packing rings to substantially fill the stuffing box to prevent or minimize the escape of the contents of the housing at the intersection of the shaft and housing. Tightening of the gland is conventionally by means of a flange through which bolts pass, and the bolts generally being threaded into threaded holes in the stuffing box. When the gland is tightened the packing rings are further compressed in the stuffing box.
Compression packing rings are frequently replaced due to daily wear and tear. Replacement of worn compression packing rings, and re-packing and/or replacement of comparatively non-compressible bushing rings or sleeves, which are both used to help fill the stuffing box in lieu of compression packing rings and to aid in the compression of the compression packing rings which are employed, is a laborious process subject to numerous calculations pertaining to the appropriate size and number of packing rings and bushings which should be employed.
The mechanic faced with packing, compressing and sealing a shaft in a stuffing box is faced with an number of variables that make the accomplishment of these tasks, on a routine basis, difficult. For example, the mechanic is faced with an extremely broad range of stuffing boxes having various inner diameters (ID) and outer diameters (OD), the possible combinations of the same running in the tens of thousands. Further, stuffing box depths can vary considerably with respect to the number of rings and sleeves needed to fill the box. The mechanic is also faced with numerous packing material types and styles that require different levels of compression in order to perform their sealing duties.
For a mechanic to appropriately pack a stuffing box, the mechanic must conventionally measure the inner and outer diameter dimensions of the stuffing box cavity, measure the stuffing box depth, select a proper packing material to be employed in the stuffing box having the correct packing cross-section (Stuffing Box Bore Dimension (OD)-Stem Diameter (ID)/2=Packing Cross-Section), determine the uncompressed stack height (=Number of Rings.times.Ring Cross-Sectional Height) and compressed stack height (=100%-Recommend Percent Compression/100 X Uncompressed Stack Height) of the selected packing material, determine the number of compression rings needed, and determine if any additional bushing rings or sleeves are required to fill the excess stuffing box depth space (Excess Box Depth=Actual Box Depth--Packing Set Compressed Height; Number of Bushing Rings Required=Excess Box Space/Cross-sectional Height of Bushings) after performing the appropriate calculations involved.
Given an adequate amount of time, the proper tools, and the proper training, a mechanic can perform all of the above steps and insure that the valves, pumps etc. that are packed are done with a high degree of accuracy. Unfortunately, this scenario is not typically the case. Mechanics are usually given a number of shafts that they are required to seal within a limited time frame. Calculation errors are not infrequent. The general location of most shafts usually does not typically lend an environment conducive to the required calculations and notes. As a result, most mechanics are required to attempt a high level of performance without the tools or time necessary to guarantee the accomplishment of the task.
There is, therefore, a need for a improved manner in which to pack a stuffing box. In particular, there is need for a quick and accurate method for packing a stuffing box without the need to make numerous calculations.